1. Field of the Invention
The present invention relates to neutral zinc-containing calcium-aluminum double salts, their preparation, use in compositions and stabilizer systems and uses thereof.
2. Description of the Background Art
Novel lead-free PVC stabilizers require hydrotalcites or zeolites as stabilizer components for long-term stabilization in rigid PVC applications.
Known long-term stabilizer components are magnesium-aluminum hydroxocarbonates (U.S. Pat. No. 4,299,759), which are in most cases prepared from water-soluble precursors with the formation of salts as by-products according to the coprecipitation method (Catalysis Today 11(2), 201-212 (1991)). However, this method is not very advantageous since the amount of contaminants in the wastewater is increased due to the additional salt impurity.
U.S. Pat. No. 4,675,356 describes zinc-containing magnesium-aluminum hydroxocarbonates.
A PVC stabilizer based on hydrotalcite and calcium-aluminum hydroxide is publicized in DE-A 1 964 1551. Furthermore, DE-A 1 952 6370 discloses mixed alkaline earth metal-aluminum hydroxides as acid scavengers during the processing of thermoplasts. However, during the synthesis, the addition of sodium hydroxide or sodium aluminate to the reaction components has proven disadvantageous since in so doing molar amounts of NaOH have to be disposed of via the wastewater.
WO-A 92/13914 claims the use of calcium-aluminum hydroxides (hydrocalumites) as stabilizers for PVC. Carbonate-containing homologs, however, are not included here since, according to the description, the desired stabilizer effect cannot be achieved with these. The synthesis takes place according to the salt method (coprecipitation). This leads in turn to additional salt impurities in the wastewater.
WO-A 93/25613 names catoites as stabilizers for chlorine-containing olefin polymers. WO-A 93/25612 describes catoites with incorporated alkali metal ions as PVC stabilizers. A starting product is in turn sodium aluminate which, following the desired reaction, in turn releases molar amounts of NaOH, as a result of which the salt content in the wastewater is increased here too.
EP-A 0 742 782 describes basic magnesium-aluminum carbonates or calcium-aluminum hydroxides which additionally comprise the heavy metals titanium, zirconium and tin as 4-valent cations. These metals are incorporated by the corresponding tetrachlorides. However, working with these compounds in large reaction vessels charged with water and other reactants is complex since the tetrachlorides are extremely hydrolysis-sensitive and acid clouds are formed in air.
There is therefore a need for further salts which can be used in particular as stabilizers for synthetic polymers such as rigid or flexible PVC.